git-touch-android-ios-app/lib/app.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter_gen/gen_l10n/S.dart';
import 'package:git_touch/models/auth.dart';
import 'package:git_touch/models/theme.dart';
import 'package:git_touch/router.dart';
import 'package:intl/locale.dart' as l;
import 'package:provider/provider.dart';

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final auth = Provider.of<AuthModel>(context);
    final theme = Provider.of<ThemeModel>(context);

    // ignore: prefer_function_declarations_over_variables
    final LocaleListResolutionCallback localeListResolutionCallback =
        (locales, supportedLocales) {
      // 1. user set locale
      // 2. system locale
      try {
        if (theme.locale != null) {
          final intlLocale = l.Locale.parse(theme.locale!);
          locales = [
            Locale.fromSubtags(
              languageCode: intlLocale.languageCode,
              countryCode: intlLocale.countryCode,
              scriptCode: intlLocale.scriptCode,
            ),
            ...locales!
          ];
        }
      } catch (err) {
        print(err);
      }

      for (final locale in locales!) {
        // this is necessary because Flutter only handles zh_Hans -> zh
        // and would not handle non-exist language code
        if (AppLocalizations.delegate.isSupported(locale)) {
          return locale;
        }
      }

      // 3. if none match, use the default
      return supportedLocales.firstWhere((l) => l.languageCode == 'en');
    };

    return Container(
      key: auth.rootKey,
      child: CupertinoApp.router(
        routeInformationProvider: router.routeInformationProvider,
        routeInformationParser: router.routeInformationParser,
        routerDelegate: router.routerDelegate,
        theme: CupertinoThemeData(brightness: theme.brightness),
        localizationsDelegates: AppLocalizations.localizationsDelegates,
        supportedLocales: AppLocalizations.supportedLocales,
        localeListResolutionCallback: localeListResolutionCallback,
      ),
    );
  }
}